This invention relates to a method for heat treating a bread baking wheat flour to form a flour, and to the resulting flour and dough having improved baking characteristics.
It has been recognized for many years that the oxidation of a wheat flour can improve the rheological and baking performance of the flour in a yeast leavened dough system. Freshly milled flours tend to produce doughs which are excessively pliable and lack the elasticity to produce optimum finished bread characteristics. When flour is stored with free access to the air, a slow oxidation process takes place which is referred to as aging or maturing of the flour. Properly matured flour produces a more lively, more elastic dough characteristic as compared to freshly milled flour. Many factors such as the degree of exposure of the flour to the air and the temperature of the air can affect the rate of oxidation of the flour. It has been suggested that pneumatic transfer of flour at the mill and the bakery accelerate the oxidation process due to the increased exposure of the flour particles to air.
The oxidation of gluten proteins in wheat flour includes the oxidation of sulfhydryl groups, which results in cross-linking of protein chains. This cross-linking inhibits the reduction and interchange of disulfide bonds. The effect of oxidation of gluten proteins on the rheological properties of dough can be demonstrated by load extension tests such as the Brabender Extensigraph test (American Association of Cereal Chemists 1983 Method 54-10). Extended aging of wheat flour results in reduced dough extensibility and increased resistance to extension using the Extensigraph test. Chemical oxidizing agents can directly or indirectly oxidize sulfhydryl groups of gluten proteins when wheat flour has been hydrated and mixed into a dough. Extensigraph tests show that chemical oxidizing agents cause wheat flour doughs to become less extensible and to increase in resistance to extension. The type and level of chemical oxidant, the amount of reaction time and the inherent properties of specific flours all influence the degree of rheological modification to the dough.
The chemical oxidizing agent aziodicarbonamide (ADA) is generally added to bleached wheat flour for bread baking at 10 ppm as a maturing agent and can be added at up to 45 ppm. At high levels of usage, ADA is considered an improver rather than a maturing agent. Up to 50 ppm of the chemical oxidizing agent potassium bromate can be added to wheat flour as an improver, and the resulting flour is referred to as bromated flour. The chemical oxidizing agent L-ascorbic acid can be added to wheat flour at levels up to 200 ppm and is considered an improver.
Chemical oxidizing agents added to flour have little or no effect on the gluten proteins until the flour is hydrated and mixed into a dough. The rate of reaction of chemical oxidizing agents in a dough varies from rapid for ADA to intermediate for ascorbic acid to slow for potassium bromate. The varying rates of reaction of various chemical oxidants in a dough system make their role in a baking process differ significantly. The rate of reaction of potassium bromate in a dough system is relatively slow and is most effective at the late proofing stages and early oven stages.
The level of chemical oxidation required in bread baking is heavily dependent on the type of process being utilized. Processes where bulk fermentation has been eliminated or reduced to a short time are often heavily dependent on chemical oxidizing agents. Straight dough processes where bulk fermentation is essentially eliminated are referred to as "no-time" straight doughs. Straight dough processes where bulk fermentation is relatively short (less than 1 hour) are referred to as "short-time" straight doughs. Both no-time and short-time straight dough processes traditionally have relied on relatively high levels of potassium bromate. Conventional straight dough processes where bulk fermentation is carried out for 11/2 to 21/2 hours have a moderate oxidation requirement. Sponge and dough processes where a sponge containing part of the total flour in the formulation is fermented for 3-5 hours, generally have relatively low oxidation requirements.
The United Kingdom and Canada have removed potassium bromate from the list of permitted food additives. In the United States many bakers have voluntarily removed potassium bromate from their formulations and replaced it with a combination of other chemical oxidizing agents.
Potassium bromate free formulations are typically less tolerant to variations in processing conditions than the same formulations containing potassium bromate. The higher the oxidation requirement of a processes, the more noticeable is the lack of tolerance that is experienced when potassium bromate is removed and replaced with combinations of other oxidizing agents, such as ADA, ascorbic acid, or potassium iodate.
In the 1920's and 1930's several researchers studied the use of heat treatment to improve the bread baking quality of wheat flour, as reported in the following documents:
Kent-Jones, D. W. "A Study of the effect of heat upon wheat and flour, especially in relation to strength". Thesis presented to London University (1926); PA1 Herd, C. W., Cereal Chem, VIII, 1 (1931); PA1 Herd, C. W., Cereal Chem, VIII, 145 (1931); PA1 Geddes, W. F., Canada. J. Res., I, 528 (1929); PA1 Geddes, W. F., Canada, J. Res., II, 195 (1930); PA1 Geddes, W. F. Canada. J. Res., II, 65 (1930); PA1 British Patent 180,496 (1922); PA1 British Patent 228,841 (1925); PA1 British Patent 300,291 (1938); PA1 British Patent 300,537 (1938).
Chemical oxidizing agents such as potassium bromate were economical and effective, and such chemical oxidizing agents became widely used.